Dryer for goods in strip or panel form

ABSTRACT

In known rack dryers, the drying effect is weaker in the outer area on the side of the air intake into the pipe chambers than in the other areas. Said weaker drying effect is caused by turbulence in this area, which leads to a drop in the static pressure. The aim of the invention is to provide a dryer which ensures even drying of the goods across the entire width, even in the problem areas. The rack dryer is equipped with conductive bodies ( 20, 26 ) which are located on the partition wall ( 5 ) and which streamline the current in the area of the air intake into the pipe chambers in such a way, that a predominantly even static pressure prevails throughout the entire pipe chamber. The invention can be used for drying sandwich-type plaster board or wood veneer.

DESCRIPTION

The invention relates to a dryer for strip- or plate-shaped material, inparticular a multilevel dryer for gypsum board or plywood.

WO 84/01424 describes an apparatus for heating or cooling foodstuffswherein an outer housing holds a blower, nozzle boxes, and a conveyorbelt. The blower is so closely juxtaposed upstream of the nozzle thatits rotation axis is generally central between the nozzle boxes. Thefeed chamber between the blower and the intake of the nozzle box isdefined by an inner housing. Between the upper and lower nozzle boxes isa hip-roof-shaped guide body. The guide body has engaging well into thefeed chamber so that the spacing of this edge from the blower onlyamounts to about one fourth of the width of the feed chamber. Such aguide body is not suitable for the dryer according to the invention.

Kroll describes in Trockner und Trocknungsverfahren (Springer; 1959;p.75ff) a dryer having a distributor wall with semicircular air-guidebodies that are arranged on the air-entry side of the chambers of adrying chamber. The distributor wall restricts the flow cross section tothe chambers, thereby increasing the pressure in the chamber, and leadsto a uniform air distribution to the individual chambers. Uniform flowin the individual chambers is not the goal. A chamber dryer is notanalogous to this art.

The invention is based on the dryer known from German 197 01 426 wherean attempt is made to create uniform drying over the entire materialwidth. This is achieved largely in that the spacing of the nozzles fromthe surface of the material is adjustable at least at one end of thenozzle box and is different at both ends. It has been shown that dryingnear the air inlet is less in the nozzle box than over the remaininglength of the nozzle box. Tests have shown that in the regionimmediately downstream of the air inlet in the nozzle box there isturbulence. This is the result of the compact construction of the dryerthat allows a relatively high vertically oriented flow speed in the feedchamber upstream of the nozzle boxes. Thus the speed in the air-entryregion in the nozzle boxes has, in addition to the horizontal, also avertical component that creates the turbulence. This means in practicethat overall the drying time is increased in order to ensure the maximalpermissible residual moisture over the entire material. Thus more energymust be used for drying than would be necessary under optimalcircumstances.

It is an object of the invention to provide a dryer with the features ofthe characterizing clause wherein more uniform drying with better energyuse is achieved on the intake side of the nozzle box.

By the use of the invention there is a uniformly directed flow withoutsignificant turbulence even in the intake region of the nozzle box. Inthe nozzle boxes the pressure relationships are largely stable so thatthe drying air can exit uniformly from all nozzles.

Preferred embodiments of the invention are given.

The drawing serves for describing the invention with reference tosimplified illustrated embodiments.

FIG. 1 shows a cross section through a dryer according to the invention;

FIG. 2 is a longitudinal section showing the partition wall;

FIG. 3 is a detail view of a guide body; and

FIG. 4 is a detail view of an alternate embodiment of a guide body.

The dryer is formed for example of a plurality of modu larly joinedsections. One section measures in the flow direction 2.0 m to 2.5 m andis 2.5 m to 6.0 m wide. As shown in FIGS. 1 and 2, it has a cover 1 andend walls 2 and 3.

In the center an intermediate floor 4, a partition 5, and a mesh-likeframe 6 define a center region 7 separate from a peripheral flowpassage. This latter is formed by a horizontal passage 8 above thecenter region 7, an end vertically extending feed chamber 9, and on theopposite side a generally mirror-symmetrical collecting chamber 10. Thewidth of the center region 7 accounts for 50 to 70% of the overallwidth, its height about 60 to 80% of the overall height. In the centerregion 7 there are a plurality, in practice at most four to twelve, oflevels that are uniformly spaced at about 250 mm to 350 mm one above theother of rollers 22 that are journaled at one side on the partition wall5 and at the other in a support frame 6. All the rollers 22 are drivenat the same speed via unillustrated gears and chains and form at eachlevel a roller conveyor that extends over the entire length of thedryer.

Below and above the conveyor levels, on which the material 11 beingdried lying on the roller conveyors is moving continuously through thedryer, there are in the spaces between adjacent rollers 22 finger-likenozzle boxes 12 that extend over the width of the roller conveyors. Thewalls of the nozzle boxes 12 facing the transport plane are providedwith nozzle openings for blowing out drying air onto the material 11 tobe dried.

One end of each nozzle box 12 is formed as an intake opening 13, and theother end 14 is closed. The nozzle boxes 12 are shaped like wedges sothat their cross-sectional size decreases steadily toward the closed end14. The end with the intake opening 13 is fitted to a rectangularaperture of the partition wall 5.

The partition wall 5 carries guide bodies 20 between two verticallyadjacent nozzle boxes 12. These project into the feed chamber 9. Theguide bodies 20 extend over the entire length of the partition wall 5.The vertical dimension H of the guide bodies 20 immediately adjacent thepartition 5 corresponds generally to the spacing between the upper edgeof the intake opening 13 of one nozzle box 12 and the lower edge of theintake opening 13 of the nozzle box 12 immediately thereabove. Thus eachguide body 20 is of neutral cross section relative to the intakeopenings 13, that is the cross-sectional size of the intake opening 13is not affected. The length L by which the guide bodies 20 project intothe feed chamber 9 is 60 mm to 100 mm, preferably 60 mm to 80 mm.

A blower 15 driven by a motor 16 is mounted in the collecting chamber 10on the side wall 2. The intake of the blower 15 is open into thecollecting chamber 10. The output of the blower 15 is connected with adiffusor 17 that opens into the horizontal passage 8. At the end of thehorizontal passage 8 opposite the blower 15 is a heat exchanger 18. Thecollecting chamber 10 and the horizontal passage 8 are separated by awall 19.

The invention is also usable with other dryers in which as a result ofcompact construction disturbing turbulence is created at the intake intothe nozzle boxes, e.g. a strip dryer. In them a meander belt can be usedinstead of a plurality of conveyors. This makes the problem ofturbulence with an increasing number of level even more apparent, inparticular with gypsum-board dryers where up to twelve levels are used.

In another embodiment of the dryer there is instead of a heat exchangerdirect heating of the drying air with a burner.

In another embodiment of the invention a guide body 20 extends over theentire width of the intake opening 13 of a nozzle box 12.

In an embodiment of the dryer for gypsum boards there are preferablybetween two adjacent transport planes an upper nozzle box 12 and anozzle box 12 directly underneath connected together in tandem so thatboth form a double box and have a common inlet opening 13.

In use the fan 15 draws drying air out of the collecting chamber 10 andpushes it through the diffusor 17 into the horizontal passage 8 in thedirection of arrow 21. At the end of this passage 8 the drying air flowsthrough the heat exchanger 18 where it is heated and then it flows intothe feed chamber 9. The flow is here from above to below and must bediverted into a nearly horizontal flow to enter into the nozzle boxes12. To this end the guide bodies 20 project into the feed chamber 9 andsmooth out the flow lines so that turbulence is avoided. The drying airis blown out of the nozzles onto the upper faces of the material 11being dried, taking water from it and flowing into the collectingchamber where it is again sucked into the fan 15. A portion of thedrying air that corresponds generally to the vaporized water is ventedfrom the circulation path.

The guide body 20 shown in section in FIG. 3 is preferably used indryers for furniture plywood. It is here shaped as a slightly upwardlybent finger. Geometrically the section of the guide body 20 is formed oftwo circle segments with offset centers. The radius R1 of the uppercircle segment 23 is 180 mm to 220 m, preferably 190 mm to 210 mm; theradius R2 of the lower circle segment 24 is 80 mm to 120 mm, preferably90 mm to 100 mm.

In another embodiment of the guide body 20 there is instead of thepointed end 25 a rounding with a radius from 10 mm to 15 mm.

The guide body shown in section in FIG. 4 is preferably used in dryersfor gypsum boards. The guide body 26 here has the shape of a rectanglewith a semicircularly rounded end, the rounded end projecting into thefeed chamber 9.

What is claimed is:
 1. A dryer for flat workpieces, the dryercomprising: a housing; an upright partition in the housing defining atreatment space and a vertical feed chamber to one side of the space,the housing having a collecting chamber to an opposite side of the spaceand a passage extending horizontally between the collecting chamber andfeed chamber; conveyor means in the treatment space for displacing theworkpieces longitudinally and horizontally through the housing in aplurality of vertically spaced levels; respective nozzle boxes extendingat the levels above and below the workpieces, having ends open at thepartition into the feed chamber, having opposite closed ends, and formedwith holes open vertically toward the workpieces; means including ablower for drawing air out of the collecting space, passing it throughthe passage to the feed space, and forcing it through the boxes and outof the holes; and respective flow-guide bodies projecting from thepartition into the feed chamber between the open nozzle-box ends.
 2. Thedryer defined in claim 1 wherein the bodies each have a curved sideturned toward the passage.
 3. The dryer defined in claim 2 wherein thecurved sides are concave toward the passage and define a sharp edgedirected generally toward the passage.
 4. The dryer defined in claim 3wherein the bodies each have a curved side turned away from the passage.5. The dryer defined in claim 4 wherein both of the curved sides havecenters of curvature lying between the respective body and the passage.6. The dryer defined in claim 5 wherein the centers of curvature of eachbody are offset from each other.
 7. The dryer defined in claim 2 whereinthe curved sides are convex toward the passage.
 8. The dryer defined inclaim 7 wherein the bodies each have another curved side turned awayfrom the passage and forming a rounded outer end on the respective body.9. The dryer defined in claim 1 wherein each of the boxes is taperedaway from the respective open end toward the respective closed end. 10.The dryer defined in claim 1 further comprising means in the housingdownstream of the blower and upstream of the boxes for heating the airmoved by the blower.